November 18, 2022
Furnace Limit Switch in Kalispell, MT

Gas furnaces have several different components to ensure that they function correctly. One of the most critical components is the limit switch, which acts as a control for the heating system and is an important safety mechanism. Let’s take a closer look at what the limit switch is and the two different functions it serves.

Controlling the Blower Fan

A furnace limit switch is located inside the supply plenum, which is where the hot air flows out of the furnace. The thermostat is the primary control for the heating system, constantly measuring the temperature inside the building to signal the furnace when to start and stop. When the thermostat tells the furnace to turn on, the limit switch signals the blower fan to operate so that it can draw cold air into the furnace. If the blower fan does not turn on, the limit switch will signal the furnace to automatically shut off so that too much heat doesn’t build up inside the unit.

Preventing Overheating

The limit switch also has a sensor that it uses to measure the temperature of the furnace and the blower fan. It will automatically shut both units down if the temperature exceeds a certain limit. This prevents electrical issues and other potential damage that can result from overheating. The limit switch is generally set to shut the system down if the furnace is above 200 F or the blower fan is above 140 F.

If the limit switch activates due to overheating, your heating system won’t turn on again until it has cooled down to a specific temperature, usually around 100 F. If your furnace ever turns off before the house is fully heated and you can’t get it to turn on again, it is likely that the system shut down due to overheating. Constant overheating can be a sign of a major issue and has the potential to seriously damage your furnace and/or blower fan.

At General Sheet Metal, Inc., we specialize in furnace inspections, repair, and maintenance, and we can also help with replacement and new equipment installations. We service air conditioning and geothermal HVAC systems, and we offer sheet metal fabrication, indoor air quality, ductwork, and thermostat services as well. If you’re having issues with your furnace overheating or need any other HVAC services in Kalispell, call General Sheet Metal, Inc. today.

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